Attenuator



Feb- 28, 1961 A. H. MAclszEwsKl ETAL 2,973,491

ATTENUATOR original Filed May 1s, 1954 United States Patent O sig'norsto A.R.F. Products,.1lnc., -River Forest, Ill., a corporation ofIllinois Griginal V:application May 13, 1954,/Ser. No. 429,547,

Ynow Patentl No. 2,881,315, dated Apr. 7, 1959. Di-

vided and this application Apr. 21, 1958, Ser. No.

Claims. (Cl 333-81) This invention relates to an attenuator andparticularly to an attenuator of the wave-guide type.

It is an important objectof the present invention to provide an improvedradio frequencyl output attenuator of. the wave guide type.

Yet another object of the invention is to prov-ide an improved radiolfrequency output attenuator which vis responsive only to the voltageinduced by the inductive coupling mode and in which the coupling can beadjusted.

-In connection with the 'foregoing object it is -a still further objectto provide an attenuator in which there is practically -no mistuning ofthe principal radio frequency tank vcircuit due to the degreeof couplingtheretoV by the attenua-tor.

Y Figure 1 -is a view in vertical section through` a. -radio frequency`output attenuator made in accordance with and embodying the principlesof the present invention;

Figure 2 is a view partially in cross section of the attenuator ofFigure 1 substantially as seen in the direction ofthe arrows along theline 2-2 of Figure l;

Figure 3 is a view `in vertical cross section ofthe atenuator of Figuresl and 2 substantially as. seenin the direction ofthe narrows along theline 3:-3 of Figure 2;

Figure 4 is an end view of the lattenuator of Figure 1 as viewed -frornthe left hand end in Figure -1 jvFigure 5v is Ian enlarged partial viewin cross section substantially as seen inthe ydirection of the arrowsalong the line 5--5 of Figure 4 and illustrating theconstructiop of thecapacitive mode suppressor; and

Figure 6 is a schematic electrical diagram of the attenuator of Figures1 to 5 and showing `the'relation thereofV to associated circuitcomponents. AReferring now particularly to Figures 1 and `6 of thedrawing, Vthere is shown an output radio frequency attenuator made yinaccordance with the lembodyi'ng'the principles of the present invention,the attenuator beingkgenerally designated by the ynumeral 191. Theattenuator includes in general apick-up coil 192, one vend of which isygrounded as at 194 and the other end 196 of which is connected to theelectronic equipment to be tested. Coil 192 is inductively coupled to anassociated coil such as a coil 134 in a tank circuit. An electrostaticshield 198 is provided to prevent excitation of the pickupY loopY orcoil 192 by capacity coupling. The pick-up coilf192is`positioned withina metal tube 200'so that the tube and coil operate on theinductive-coupling mode as a wave guide below cuto.

A pick-up loop or monitor wire 202 vis provided, the monitor wireextending into the tube 200 and being positioned between the pick-uploop 192 and the electrostatic shield 198. The position of the monitorloop 202 is adinstable.w A connection is made from the monitor Ioop 2,02through a rectifier 204, a resistance 206 a Airst invductance 208 and asecond inductance '21.0 to a speaker. `A capacitor 212 by-passes rtheresistance 206 to ground.

'l g rThe wave guidebtube 200 is preferably circular in cross sectionVand is open at both ends, one end being provided g 2,973,491y PatentedFeb. 2s, 1196i with an outturned attachrent lia-nge 214 which Lis toattach the attenuator lto the @chassis of the signa-l generator.Theother end of tube 200 has a plurality lof slots formed therein whichreceive three at pieces or straps of metal 216 which form theelectrostatic shield 198. From lFig. 4 it will be seen that the straps216 are disposed parallel with each other with the center strap lyingalong a diameterof tube 200. y*It will be further seen thatthejorientation of the straps 216 is `in a plane perpendicular to thelongitudinal axis of the ymonitor wire 202. The shape in planview of thestraps 216 is vvbest seen in Fig. 5, the straps being 'substantiallyrectangular `insl'1ape but having va semi-'circular cut-out 218 alongone of Athe-"longer edges thereof, the cut-out 'being along 'the edgepositioned inwardly of tube 200 and being positioned about thelongitudinal center l-ine ofv tube 200.

The upper side of tube 200 'as viewed in Fig. 1 has an Ielc'mgated slotl220 formed therein through which monitor wire `202 lextends. Monitor'wire 202 is xedly attached to the 'end of :a second tube 222 whoseexternal diameter -is slightly less than the linternal diameter of tube200 whereby 'tube 222 slides easily within tube 200. An abutment member224 positioned on tube 222 extends upwardly through fsl'ot '220 andserves to center tube 222 with respect to slot 220 and `thus in turncenters the monitorwire202. The vother end of tube 202 carries a collar226 viixedly 'attached thereto which includes the adjust-ing mechanismthat will be described later.

Positioned within vtube 222 and slidable therein is a substantiallycylindrical plunger 228. The left hand end of plunger 228 as viewed inFig. l has Va longitudinal aperture therein which receives ra resistor230. One en'd of resistor 230 is attached to plunger 228 in apart-circular depression therein as at 232 andthe other end- -ofresistor 230 is connected to the pick-up loop 192. A longitudinal holethrough `plunger v228 Areceives `'a co-axial cable 234 which has the'center lead 196 therein attached to 'one end of the pick-up loop 192.The other end of the co-axial cable 234 is provided with the usualcoupling 236. i

In the actual installation the 'end of the tube 200 carrying theelectrostatic shield straps 216 is positioned adjacent tothe coil in thetank of a variable frequency oseillator. tI-t is desirable to adjust theradio frequency -iniection into the attenuator by moving the monitorWire 202 and' the pick-niploop 192 toward and away Vfrom the shield andstraps 216 and the associated feed coil. Also' ing the desired movementof tube 222 and plunger 228 The portion of tube 222 will be described indetail. which normally extends outwardly and to the 'right with respectto iiange 214 'as viewed in Fig. 2 has attached thereto by means ofscrews 238 a geared rack 240. A gear 242 mounted on a shaft 244 isprovided vto engage with rack 240.

Shaft 244 is permanently positioned with respect to iiange 214 and arotary movement of shaft 244 and the attached gear 242 causes-movementof tube 222 inwardly and outwardly with respect to tube 200. Thisaccordingly adjusts the position of monitor wire 202 with 're` spect tothe associated tank coil, this adjusting motion -being vaccomplishedwithout aliecting the attenuation be- I y *waarnaar to tube 222 ismounted on the upper Aportion of member 226 as viewed in Figs. 2 and 3.A slot 246 is formed in plunger 228 at the righthand thereof as viewedin Fig. 2 and within the slot is mounted a geared rack v248 held inposition by two screws 250. vThe highest point on the teeth of rack 248is-disposed well within the circumference oftube 228. A slot is formedat the night hand end of tube 222 and into this slot extends a toothedgear 252 which cooperates and meshes with the teeth on .rack 248. Gear252 is mounted on a -rotating shaft 254 which is journaled in a pair ofbearing blocks 256. In order to insure that there is no lost motion inthe gear and rack arrangement, a frame 258 is provided that supports apair of springs 269 that are under compression. AThe springs 260 pressagainst 'the bearing blocks 256 and thus `in turn press gear 252 againstrack 248 to eliminate lost-motion and inadvertent misadjustmenttherebetween.

The attenuator of Fig. 1 through 5 insuresthat .only the desiredexcitation is obtained on pick-up loop 192, the desired excitation beingthat corresponding to the inductive coupling mode. This is obtained byproviding the electrostatic shield Y 198 including the straps 216`between the associated feed coil vof the RF tank and the pick-up loop192. Since the electrostatic shield 198 is immobile and since themonitor loop moves behind the shield, there is practically no mistuningof the main RF tank including the associated feed coil due to the varia-.tions of the position of the monitor loop 202. Further- ,i

more, the amount of RF injection into the attenuator can 1be adjusted byturning shaft 244 without affecting the value of the attenuation Aandthe value of the attenuation can Ibe adjusted by turning shaft 254thereby changing the distances between pick-uploop 192 and the moni- Istwill be seen that there has been provided an attenuiator of the waveguide type which fulfills all of the adtvantages and objects set forthabove. ciic example of the attenuator has been given for pur- Although aspeposes of illustration, it is to be understood that various .changescan -be made therein without departing from the spirit-and scope of theinvention. Accordingly, the in- .vention is to be limited only as setforth in the follow- .ing claims.

. We claim:

1. A radio frequency attenuator for operation with an `associated sourceof radio frequency radiation on the .inductive-coupling mode as a waveguide below cutoff, V`comprising a first tube adapted to have one of theopen ends thereof disposed toward'and xedly positioned with .respect tothe radiation source, said rst tube having a longitudinal slot therein,a second tube positioned within said first tube and being slidablyadjustable therein, a

monitor member mounted on and carried by said second 'through said slota distance that is small compared to 'the transverse dimension of saidiirst tube whereby said monitor member is inductively coupled to theradiation jsource, means positioned in said one end of said rst K ,tubeforming an electrostatic shield suppressing the capacitive-couplingmode' between said monitor member and the radiation source, a pickupmember positioned within said second tube and being slidably 'adjustableftherein to receive'radiation from said monitor member, lrst adjustmentmeans to move said second tube including said monitor member and saidpickup member si- ,multaneously with respect to said first tube toadjust the amount of radiation injected into said attenuator withoutchanging the attenuation betweenv said monitor member and said pickupmember, and second adjustment means to move said pickup member withrespect to said 'monitor member without moving said monitor member .tubewithin said first tube and extending outwardly Y' .respect to theradiation source,

with respect to said rst tube whereby to adjust the attenuation betweensaid monitor member and said pickup member without changing the amountof radiation injected into said attenuator.

2. A radio frequency attenuator for operation with an associated sourceof radio frequency radiation on the inductive-coupling mode as a Waveguide below cutoff, comprising a rst tube adapted to have one of theopen ends thereof disposed toward and fixedly positioned with respect tothe radiation source, said rst tube having a longitudinal slot therein,a second tube positioned within said rst tube and being slidablyadjustable therein, a monitor member mounted on and carried by saidsecond tube `within said lirst l,tube and extending outwardly throughsaid slot a distance that is small compared to the transverse dimensionof said rst tube whereby said monitor member is inductively coupled tothe radiation source, an abutment member lixedly mounted on said secondtube and extending into said slot and engaging the edges thereof to holdsaid monitor member spaced from the edges of said slot, a plurality ofmetal straps mounted across said one end of said first tube to providean electrostatic shield suppressing the capacitive-coupling mode betweensaid monitor member and the radiation source, a plunger positionedwithin said second tube and being slidably adjustable therein, a pickupmember mounted on said plunger within said second tube to receiveradiation from said monitor member, first adjustment means to move saidsecond tube and said plunger simultaneously with respect to said rsttube thereby to move simultaneously said monitor member and said pickupmember with respect to the associated radiation source to adjust theamount of radiation injected into said attenuator without changingtheattenuation between -said monitor member and said pickup member, andsec- ,ond adjustment means to move said plunger with respect to saidsecond tube thereby to move said pickup member toward and away from saidmonitor member without moving said monitor member with respect to saidfirst tube whereby to adjust the attenuation between said monitor memberand said pickup member without changing the amount of radiation injectedinto said attenuator.

3. The radio frequency attenuator as set forth in claim 2, wherein themonitor member is a wire, and the straps lare positioned along chordallines of the first tube and are disposed perpendicular to the axis ofsaid monitor -w1re.

4. A radio frequency attenuator for operation with an associated sourcevof radio frequency radiation on the inductive-coupling mode as a waveguide below cutoff, ycomprising a first tube adapted to have one of theopen ends thereof disposed toward and ixedly positioned with said firsttube lhaving a longitudinal slot therein, a second tube positionedWithin 'said rst tube and being slidably adjustable therein, a

'monitor member mounted on and carried by said second tube within saidfirst tube and extending outwardly through said slot a distance that issmall compared to :the transverse dimension of said first tube wherebysaid .monitor member is inductively coupled to the radiation source,means positioned in said one end of said first tube forming anelectrostatic shield suppressing the capacitive-coupling mode betweensaid monitor member and the radiation source, a plunger positionedwithin said second tube and being f slidably adjustable therein, apickup member mounted on and carried by saidplunger within said secondtube and'positioned to receive radiationfrom said monitor member, rstadjustment means including a first rack and pinion acting between saidfirst and second tubes to move said second tube including said monitormember and said plunger including `said pickup member simultaneouslywith respect to said first tube to adjust the amount of radiationinjected into said Aattenuator without changing the attenuation betweensaid t monitor member and said pickup member, and second adjustmentmeans including a second rack and pinion one end thereof connectedthrough a resistor to said acting between said second tube and saidplunger to plunger and having the other end thereof connected to movesaid pickup member with respect to said monitor the center conductor ina radio frequency co-axial cable member without moving said monitormember with carried bythe plunger.

respect to said `i'irst tube whereby to adjust the attenuao ReferencesCited in the me of this patent tion between said monitor member and saidpickup member without changing the amount of radiation injected UNITEDSTATES PATENTS into said attenuator. 2,494,722 Rosen J an. 17, 1950 5.The radio frequency attenuator set forth in Claim 2,666,183 OcnaschekJan. 12, 1954 4, wherein the pickup member is a loop of wire having 102,701,863 Pierce Feb. 8, 1955

